The α-factor pheromone receptor stimulates MATa yeast cells to undergo conjugation. The receptor contains seven transmembrane domains that function in ligand binding and in transducing a signal to the cytoplasmic receptor sequences to mediate G protein activation. A genetic screen was used to isolate receptor mutations that constitutively signal in the absence of α- factor. The Pro-258 → Leu (P258L) mutation caused constitutive receptor signaling that was equivalent to about 45% of the maximum level observed in wild-type cells stimulated with α-factor. Mutations of both Pro-258 and the adjacent Ser-259 to Leu increased constitutive signaling to ≤90% of the maximum level. Since Pro-258 occurs in the central portion of transmembrane domain 6, and since proline residues are expected to cause a kink in α- helical domains, the P258L mutation is predicted to alter the structure of transmembrane domain 6. The P258L mutation did not result in a global distortion of receptor structure because α-factor bound to the mutant receptors with high affinity and induced even higher levels of signaling. These results suggest that sequences surrounding Pro-258 may be involved in ligand activation of the receptor. Conformational changes in transmembrane domain 6 may effect a change in the adjacent sequences in the third intracellular loop that are thought to function in G protein activation. Greater than 90% of all G protein-coupled receptors contain a proline residue at a similar position in transmembrane domain 6, suggesting that this aspect of receptor activation may be conserved in other receptors.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Jun 25 1996|
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